Here’s a summary of what we’ve discovered so far: The basic sus chord is derived from the major triad, which is composed of the 1, 3, and 5 of a major scale built from the same root. When you replace the major triad’s 3 with either the 2 or 4 of that major scale, you create a sus2 or sus4 voicing. The resulting 1-2-5 or 1-4-5 construction creates a compelling harmonic tension that’s resolved when the 2 or 4 swings back to the 3.
So far, we’ve been operating in an “either/or” mode—that is, we’ve had the 3 or the 2 or 4 in a given voicing. Shifting between the 3 and the suspended tone is what generates harmonic interest. You can, however, create a voicing that includes both the 3 and the 2 or 4. Because you’re adding a color (rather than swapping it for the 3), these are called add2 or add4 chords. To hear these rich and prickly harmonies, play
Examples 1 and 2, which feature Gadd4, Dadd2, and Aadd2 voicings.
For the best of all worlds, try integrating sus and add voicings, as in Ex. 3. Here, we explore the back-and-forth movement of sus chords before concluding with an edgy Dadd4,9. This final voicing offers everything: the 1, 3, and 5 of a D major triad (D, F#, A), as well as its 2 (E)—played here an octave higher as an extension, which makes it a 9—and 4 (G). Don’t freak out over the sixteenth-notes in bar 2, beat three. In harplike fashion, simply strum across the strings to get a rippling effect. Play that last open A softly, so it doesn’t overwhelm the other sustaining notes.